AYCL-153P Dimmer not working correctly

I have four AYCL-153P Dimmers in my house. None are working correctly. When the switch is ON and I slide the SLIDER up and down, the light does not dim (or brighten). However; when I remove the faceplate and push the ADJUSTMENT DIAL left or right, then the light will dim (or brighten). I have tested the switch with the ADJUSTMENT DIAL on several settings, but the SLIDER does not work. Why is this?I replaced one of the AYCL-153P Dimmers with a new one and it works perfectly. Are the older dimmers at end of life? Or are they faulty? What would cause them to stop working correctly?Thank you, Joe

Older models had wire pigtails instead of screw terminals like newer models. Make sure the power is coming in on the black wire and out to the lights on the red wire. The red/white wire is only used if you have additional 3-way/4-way switches.

The dial sets the high/low (minimum and maximum) end trim.

If they are wired correctly, it could be the dimmer has failed.